Several warning methods for alerting populations to weather, emergencies and civil disasters are in use at the present time. Shortcomings and deficiencies of those considered below are indicated.
Television stations superimpose messages on normal programming or interrupt normal programming to advise their viewers of severe weather conditions. One major deficiency of this warning method is that the region of coverage of the typical local television station (i.e., the region over which the signals transmitted by the local television station are received) is so extensive that the severe weather condition warnings are received in areas within the region of coverage that are not exposed to and will not be affected by the severe weather conditions being reported by the local television station. At best, this is a nuisance to those individuals who hear the alerts but are not, and will not be, affected by the severe weather conditions being reported. Also, this warning method requires that the television receivers be turned on, actively watched, and tuned to a local television station that is broadcasting the severe weather condition warning for the warning to be received and viewed.
Another example of a warning system currently in use many communities to warn residents of emergencies is a controlled siren, commonly referred to as a civil defense or air raid siren. Such systems are susceptible to mechanical breakdowns and must be taken out of service periodically for routine maintenance. Also, such systems are ineffective to give warnings to those located out of range of the sirens.
Yet another example of a warning method currently in use in many communities is police and fire departments patrolling the streets and announcing warnings or emergencies over loudspeakers. This method is ineffective when the warning message from the loudspeaker is not heard by those located out of range of the loudspeaker or the warning message is drowned out by weather noise or interfering noise levels in the residences where the warnings are intended to be received by individuals situated in the residences.
In a special purpose warning system, currently in use by the National Weather Service, continuing weather bulletins are broadcast on a VHF frequency front transmitters of the National Weather Service. Whenever severe weather threatens, an alert is broadcast that triggers an audible alarm in special receivers, such as the weather radio units available from Tandy Corporation. Because the coverage areas of the broadcast stations usually are quite large (i.e., a National Weather Service facility can cover and be responsible for as many as ten to twenty counties), it is possible, as with the broadcasting of severe weather condition warnings by local television stations, to receive alerts on a receiver in an area to which the alerts have no actual significance. Again, at best, this is a nuisance to those individuals who hear the alerts but are not, and will not be, affected by the severe weather conditions being reported. Additionally, when an alert is triggered in such a receiver, it must be muted manually by the user because the system does not have a broadcast “all clear” signal.
U.S. Pat. No. 5,121,430 describes and illustrates a system designed to overcome the shortcomings identified above of the special purpose warning system described above. The system described in U.S. Pat. No. 5,121,430, however, requires extra, specially designed equipment dedicated to the single purpose of receiving and processing the transmitted warning signals.